Dietary protein requirements of the juvenile swimming crab, Portunus trituberculatus

An 8-week feeding trial was conducted to determine the optimal dietary protein requirements for juvenile swimming crabs (Portunus trituberculatus) reared in cement pools. Six iso-energetic and iso-lipidic experimental diets were formulated to contain graded levels of protein, and these dietary protein levels were 31.6, 36.5, 41.7, 45.6, 50.2 and 55.8% of the dry matter, respectively. Each diet was randomly assigned to triplicate groups of 60 juvenile swimming crabs (approximately 2.50 ± 0.08 g) that were stocked in rectangle plastic baskets. The results indicated that dietary protein had a significant effect on weight gain, specific growth rate, protein productive value, feed conversion ratio and protein efficiency ratio, and maximal weight gain and specific growth rate were obtained at 50.2% dietary protein. No mortality was found among all treatments. Dietary protein had a significant effect on whole-body crude protein, total lipid, moisture content and on muscle amino acid profile; and a positive correlation was observed between EAA concentrations in muscle and dietary protein levels, however, there was no significant difference in ash content of whole body. The optimal dietary protein requirement, estimated by two slope broken-line model based on specific growth rate against dietary protein levels, was 51.5% of the dry matter for juvenile swimming crabs.